Inhalation anesthetics augment oxidant-induced pulmonary vasoconstriction: Evidence for a membrane effect

Inhalational anesthetics 'fluidize' biologic membranes. Since arachidonate metabolism also occurs in cell membranes, anesthetic agents may modify arachidonic acid metiator production. The authors used the isolated perfused rabbit lung preparation to examine the effects of inhalational anesthetics on the production of arachidonate mediators. The oxidant tert-butyl-hydroperoxide (t-bu-OOH) is known to cause pulmonary vasoconstriction by causing increased production of thromboxane A₂ (TxA₂). The authors administered three anesthetics (halthane, cyclpropane, and nitrous oxide) of widely different potencies, at different dosages, each to three different groups of preparations and challenged the lungs at each anesthetic dose with t-bu-OOH. They found a dose-related augmentation of the pulmonary vasopressor response to t-bu-OOH. Preparations given t-bu-OOH alone showed no change in response over time. Lungs perfused with indomethacin (5 μg· ml^-1 in Krebs-Henseleit buffer), ventilated with cyclopropane (2 MAC), and challenged with t-bu-OOH showed almost complete inhibition of the response to t-bu-OOH. Indomethacin at this concentration is a specific inhibitor of cyclooxygenase. The authors also demonstrated significantly increased perfusate levels of thromboxane B₂ (TxB₂), the inactive metabolite of TxA₂, after oxidant challenge during exposure to 2% halothane compared with TxB₂ levels before halothane exposure. The authors believe that the augmented pressor response and mediator production occur because of increased substrate (arachidonic acid) availability induced by anesthetic agent.